Kranz Anatomy and the C 4 Pathway

Abstract

Abstract C 4 photosynthesis incorporates novel leaf anatomy, metabolic specializations and modified gene expression. Plants that utilize this pathway typically possess a distinctive Kranz (or wreath) leaf anatomy, consisting of two photosynthetic cell types. These are the bundle sheath (bs) cells, which surround the vascular centres, and the mesophyll (mp) cells, which surround the bs cells. This structural framework allows for the compartmentalization and functional separation of two sets of carboxylation and decarboxylation reactions. Within C 4 leaves, selective expression of bs and mp cell‐specific genes leads to the selective accumulation of key photosynthetic enzymes which catalyse the different sets of cell‐type‐specific reactions, thereby enabling these plants to assimilate atmospheric carbon dioxide with very high efficiency. For some plants, C 4 photosynthesis has facilitated their adaptation to arid conditions, high temperatures and marginal environments. Understanding the basis of this pathway has applications for improvements in agricultural productivity and alternative fuel development.